Gene Vogel
EASA Pump & Vibration Specialist

Vibration has three primary parameters; amplitude, frequency and phase. Previous presentations and papers have focused on the two most common parameters, amplitude and frequency. These two are the primary tools for determining if a machine vibration is a problem, and what the cause of the vibration might be. This paper, presented at the 2013 EASA Convention, focuses on the third parameter: phase angle.

While vibration phase angle has several perspectives, this paper focuses on the most straightforward aspect — the angular relationship between vibratory motions of two different locations on a machine. Inherently, then, phase angle is based on two different inputs and measuring phase requires two input signals. The two signals can be two vibration transducers, or a single vibration transducer and a reference pulse signal from a photo tach, laser tach, key phasor or such. For those who are familiar with using a strobe light and a single transducer to measure phase angle, your eye and the reference mark on the shaft provide the second input.

Phase angle is seldom used to detect when a problem occurs on a machine. But it is a powerful tool for diagnosing vibration in many common situations. It also provides necessary data for dynamic balancing. For phase to be useful in any situation, it must be coupled with the corresponding vibration amplitude. Together, phase and amplitude constitute a vector. A basic understanding of vectors is fundamental to vibration analysis.

This paper covers:

• Amplitude and phase concepts
• Shaft alignment vector analysis
• Planar shape sketches
• Animated Operating Deflection Shape (ODS)
• ODS instrumentation and software

Vibration data from field measurements can tell a great deal about the health of machine components and required follow-up action. Beyond acquired time waveform or spectral frequency pattern data, several tools are available in most portable vibration instruments to determine natural frequencies, shaft centerline motion, and the relative movement of machine components. Drawing on practical examples, this paper will also cover:

• Startup/coast down analysis
• Bump tests
• Cross-channel phase measurement
• Demodulation techniques
• Orbital plots

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Categories: Vibration, Convention presentations, 2013

Tags: Vibration

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